9 This proposal will use psychophysical techniques, together with computational modeling, to study binocular rivalry, the breakdown in stable binocular single vision resulting from discordant monocular inputs. During rivalry the eyes convey contradictory information to the brain about the nature of objects at given locations in visual space. Faced with rival interpretations, the brain lapses into an unstable state characterized by fluctuations in perception that continue as long as the eyes view discordant stimuli. The study of binocular rivalry, as well as other forms of multi-stable perception, bears importantly on a number of key issues in vision science: perceptual organization, dynamical systems, visual awareness, attention and, possibly, neural bases of strabismic suppression (a developmentally-based disorder of binocular vision that affects an estimated 5% of the population). Interest in binocular rivalry has grown considerably in recent years, sparked in part by previous work from the Pi's laboratory. Still, important issues remain unresolved, issues concerning the determinants of rivalry and its underlying neural bases. Building on earlier work supported by EY13358, the proposed studies will explore several of these issues: a) the role of neural adaptation in triggering the instability of rivalry dominance (dynamics), a problem highlighted by computational models of rivalry, b) the residual effectiveness of a suppressed stimulus as revealed by visual adaptation aftereffects (suppression), c) determinants of initial dominance in rivalry (selection), with particular emphasis on affective and attentional factors, and d) the influence of attention on rivalry dominance (predominance), an influence implied by recent accounts of rivalry. Using psychophysical techniques paired with quantitative modeling, the proposed experiments will resolve outstanding controversies concerning rivalry, including the role of neural adaptation and "top-down" cognitive factors in selection, dominance and suppression. Among the psychophysical techniques is a new, objective procedure for creating records of rivalry dynamics. Results from these studies will guide refinement and amalgamation of recent computational models of rivalry and will test predictions from a newly proposed account of binocular suppression. Finally, results from these experiments will guide neurophysiologists and cognitive neuroscientists seeking to discover the actual neural concomitants of multi-stable perception.